`RedirectFromPageWithContentIP6` test locks if CONFIG_IPV6 is disabled in the Linux kernel

[Tachi107]

When the Linux kernel is built without IPV6 support, the RedirectFromPageWithContentIP6 test never completes, as it doesn't go past while(!svr.is_running()) (line 974).

cpp-httplib/test/test.cc

Lines 955 to 1013 in 3c52238

	TEST(RedirectFromPageWithContentIP6, Redirect) {
	Server svr;
	svr.Get("/1", [&](const Request & /*req*/, Response &res) {
	res.set_content("___", "text/plain");
	// res.set_redirect("/2");
	res.set_redirect("http://[::1]:1234/2");
	});
	svr.Get("/2", [&](const Request &req, Response &res) {
	auto host_header = req.headers.find("Host");
	ASSERT_TRUE(host_header != req.headers.end());
	EXPECT_EQ("[::1]:1234", host_header->second);
	res.set_content("Hello World!", "text/plain");
	});
	auto th = std::thread([&]() { svr.listen("::1", 1234); });
	while (!svr.is_running()) {
	std::this_thread::sleep_for(std::chrono::milliseconds(1));
	}
	// Give GET time to get a few messages.
	std::this_thread::sleep_for(std::chrono::seconds(1));
	{
	Client cli("http://[::1]:1234");
	cli.set_follow_location(true);
	std::string body;
	auto res = cli.Get("/1", [&](const char *data, size_t data_length) {
	body.append(data, data_length);
	return true;
	});
	ASSERT_TRUE(res);
	EXPECT_EQ(200, res->status);
	EXPECT_EQ("Hello World!", body);
	}
	{
	Client cli("http://[::1]:1234");
	std::string body;
	auto res = cli.Get("/1", [&](const char *data, size_t data_length) {
	body.append(data, data_length);
	return true;
	});
	ASSERT_TRUE(res);
	EXPECT_EQ(302, res->status);
	EXPECT_EQ("___", body);
	}
	svr.stop();
	th.join();
	ASSERT_FALSE(svr.is_running());
	}

I believe that this happens because when IPV6 support isn't available svr.listen("::1", 1234) never actually starts anything, so the condition !svr.is_running() will always remain true.

A possible solution would be to only wait for a few seconds, and if svr does not start abort the test

Edit: Since Server::listen() returns false on failure, it may be more appropriate to do something like ASSERT_TRUE(svr.listen("::1", 1234))

Edit2: ASSERT_TRUE in the other thread doesn't work